Method and system for laser ignition control

ABSTRACT

Methods and systems are provided for closed-loop adjusting a laser intensity of a laser ignition device of a hybrid vehicle. The laser intensity applied over consecutive laser ignition events is decreased until a flame quality is degraded for a threshold number of cylinder combustion events. The laser intensity is then increased to improve flame quality and the closed-loop adjustment is reiterated.

FIELD

The present application relates to methods and systems for improvingvehicle fuel economy by reducing laser energy usage of an engine laserignition system.

BACKGROUND AND SUMMARY

Engine systems on vehicles, such as hybrid electric vehicles (HEV) andvehicles configured for idle-stop operations, may be configured with alaser ignition system. In addition to initiating cylinder combustion,the laser ignition system may be used during engine starting toaccurately determine the position of a piston in each cylinder, enablingan appropriate cylinder to be selected for a first combustion event. Assuch, this improves the engine's ability to restart. The laser ignitiondevice may be continually operated at high energy intensity to ensurethat each combustion event has good combustion of the air-fuel mixture.However, since the laser ignition system uses energy from a vehiclesystem battery, frequent firing of the laser can deplete the battery. Inhybrid vehicles, this can adversely affect vehicle fuel economy.

One example approach for improving fuel economy, when using a laserignition system, is shown by Woerner et al. in US 2013/0098331. Therein,optimum burn-through of a cylinder air-fuel mixture is achieved byirradiating an ignition location inside a pre-combustion chamber with aplurality of laser ignition pulses temporally offset from one another.This allows a flame core generated in the pre-combustion chamber to beadvantageously used to ignite the air-fuel mixture of the pre-combustionchamber as well as the main combustion chamber, thereby reducing overalllaser ignition usage.

However, the inventors herein have recognized potential issues with suchan approach. As one example, the approach may not be applicable inengine systems where each combustion chamber is not coupled to acorresponding pre-combustion chamber. As another example, if the flamecore in the pre-combustion chamber is not generated correctly, inaddition to the laser energy expended in generating the pre-combustionchamber flame core, further laser energy may need to be expended togenerate a combustion chamber flame core. As such, this may increasebattery charge consumption and degrade fuel economy.

In one example, some of the above issues may be addressed by an enginemethod comprising, dynamically adjusting a laser intensity of an enginelaser ignition device during a cylinder ignition event based on amonitored cylinder flame quality. In this way, the laser intensity ofthe laser ignition system can be reduced until flame quality is affectedto improve battery consumption.

For example, an engine in a hybrid electric vehicle may be configuredwith a laser ignition system including a battery-operated laser ignitiondevice for igniting an air-fuel mixture and a photodetector formonitoring a flame quality inside each cylinder. Over a drive cycle, thelaser intensity of the laser ignition device may be reduced (e.g,step-wise) over each ignition event while the photodetector is used tomonitor the flame quality at each corresponding cylinder combustionevent. The step-wise reduction may be based on, for example, engineload, cylinder head temperature, and combustion air-fuel ratio. Thephotodetector may include, for example, an infrared sensor and/or CCDcamera for inferring a flame quality based on the peak in-cylindertemperature achieved during cylinder combustion following each ignitionevent. If the peak in-cylinder temperature achieved is lower than athreshold, it may be determined that good combustion did not occur (e.g.insufficient combustion occurred). In response to a threshold number ofconsecutive degraded flame events (e.g., 1-2 consecutive degraded flameevents), it may be inferred that the laser energy is too low forcombustion and the intensity of the laser ignition device may beincreased to improve the combustion. Then, the reduction of laserintensity may be reiterated, for example, with a smaller drop in laserintensity at each ignition event. This allows for optimal laser energyusage.

In this way, laser ignition intensity may be dynamically adjusted over avehicle drive cycle to reduce battery consumption. By reducing the laserignition intensity as much as possible without affecting flame quality,laser energy consumption is reduced. By using a closed-loop adjustmentof laser intensity based on flame quality, rather than an open-loopadjustment that over-compensates laser energy to always guarantee highflame quality, significant laser energy wastegate is reduced. As such,this reduces battery consumption and improves fuel economy in a hybridvehicle system.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a schematic diagram of an example internal combustionengine configured with a laser ignition system.

FIG. 2 shows a high level flow chart of a method for modulating theintensity of a cylinder laser ignition device based on flame quality.

FIG. 3 shows an example closed-loop adjustment to the laser energy of alaser ignition device, according to the present disclosure.

DETAILED DESCRIPTION

Methods and systems are provided for adjusting the laser energy of alaser ignition device in an engine system configured with a laserignition system, such as the engine system of FIG. 1. A controller maybe configured to perform a control routine, such as the routine of FIG.2, to feedback adjust the laser energy used during consecutive ignitionevents based on a cylinder combustion flame quality monitored by aphotodetector coupled to the laser ignition device. The laser energyused may be gradually reduced until the flame quality degrades followingwhich the laser energy may be increased. FIG. 3 illustrates an exampleadjusting of a laser ignition device intensity to reduce batteryconsumption.

Referring to FIG. 1, the figure shows a schematic diagram of an examplecylinder of multi-cylinder internal combustion engine 20. Engine 20 maybe controlled at least partially by a control system includingcontroller 12 and by input from a vehicle operator 132 via an inputdevice 130. In this example, input device 130 includes an acceleratorpedal and a pedal position sensor 134 for generating a proportionalpedal position signal PP.

Combustion cylinder 30 of engine 20 may include combustion cylinderwalls 32 with piston 36 positioned therein. Piston 36 may be coupled tocrankshaft 40 so that reciprocating motion of the piston is translatedinto rotational motion of the crankshaft. Crankshaft 40 may be coupledto at least one drive wheel of a vehicle via an intermediatetransmission system. Combustion cylinder 30 may receive intake air fromintake manifold 45 via intake passage 43 and may exhaust combustiongases via exhaust passage 48. Intake manifold 45 and exhaust passage 48can selectively communicate with combustion cylinder 30 via respectiveintake valve 52 and exhaust valve 54. In some embodiments, combustioncylinder 30 may include two or more intake valves and/or two or moreexhaust valves.

In this example, intake valve 52 and exhaust valve 54 may be controlledby cam actuation via respective cam actuation systems 51 and 53. Camactuation systems 51 and 53 may each include one or more cams and mayutilize one or more of cam profile switching (CPS), variable cam timing(VCT), variable valve timing (VVT) and/or variable valve lift (VVL)systems that may be operated by controller 12 to vary valve operation.To enable detection of cam position, cam actuation systems 51 and 53should have toothed wheels. The position of intake valve 52 and exhaustvalve 54 may be determined by position sensors 55 and 57, respectively.In alternative embodiments, intake valve 52 and/or exhaust valve 54 maybe controlled by electric valve actuation. For example, cylinder 30 mayalternatively include an intake valve controlled via electric valveactuation and an exhaust valve controlled via cam actuation includingCPS and/or VCT systems.

Fuel injector 66 is shown coupled directly to combustion cylinder 30 forinjecting fuel directly therein in proportion to the pulse width ofsignal FPW received from controller 12 via electronic driver 68. In thismanner, fuel injector 66 provides what is known as direct injection offuel into combustion cylinder 30. The fuel injector may be mounted onthe side of the combustion cylinder or in the top of the combustioncylinder, for example. Fuel may be delivered to fuel injector 66 by afuel delivery system (not shown) including a fuel tank, a fuel pump, anda fuel rail. In some embodiments, combustion cylinder 30 mayalternatively or additionally include a fuel injector arranged in intakepassage 43 in a configuration that provides what is known as portinjection of fuel into the intake port upstream of combustion cylinder30.

Intake passage 43 may include a charge motion control valve (CMCV) 74and a CMCV plate 72 and may also include a throttle 62 having a throttleplate 64. In this particular example, the position of throttle plate 64may be varied by controller 12 via a signal provided to an electricmotor or actuator included with throttle 62, a configuration that may bereferred to as electronic throttle control (ETC). In this manner,throttle 62 may be operated to vary the intake air provided tocombustion cylinder 30 among other engine combustion cylinders. Intakepassage 43 may include a mass air flow sensor 120 and a manifold airpressure sensor 122 for providing respective signals MAF and MAP tocontroller 12.

Exhaust gas sensor 126 is shown coupled to exhaust passage 48 upstreamof catalytic converter 70. Sensor 126 may be any suitable sensor forproviding an indication of exhaust gas air/fuel ratio such as a linearoxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), atwo-state oxygen sensor or EGO, a HEGO (heated EGO), a NO_(x), HC, or COsensor. The exhaust system may include light-off catalysts and underbodycatalysts, as well as exhaust manifold, upstream and/or downstreamair/fuel ratio sensors. Catalytic converter 70 can include multiplecatalyst bricks, in one example. In another example, multiple emissioncontrol devices, each with multiple bricks, can be used. Catalyticconverter 70 can be a three-way type catalyst in one example.

Controller 12 is shown in FIG. 1 as a microcomputer, includingmicroprocessor unit 102, input/output ports 104, an electronic storagemedium for executable programs and calibration values shown as read onlymemory chip 106 in this particular example, random access memory 108,keep alive memory 109, and a data bus. The controller 12 may receivevarious signals and information from sensors coupled to engine 20, inaddition to those signals previously discussed, including measurement ofinducted mass air flow (MAF) from mass air flow sensor 120; enginecoolant temperature (ECT) from temperature sensor 112 coupled to coolingsleeve 114; in some examples, a profile ignition pickup signal (PIP)from Hall effect sensor 118 (or other type) coupled to crankshaft 40 maybe optionally included; throttle position (TP) from a throttle positionsensor; and absolute manifold pressure signal, MAP, from sensor 122. TheHall effect sensor 118 may optionally be included in engine 20 since itfunctions in a capacity similar to the engine laser system describedherein. Storage medium read-only memory 106 can be programmed withcomputer readable data representing instructions executable by processor102 for performing the methods described below as well as variationsthereof.

Engine 20 further includes a laser ignition system 92. Laser ignitionsystem 92 includes a laser exciter 88 and a laser control unit (LCU) 90.LCU 90 causes laser exciter 88 to generate laser energy. Laser ignitionsystem 92 may be battery-operated in that laser exciter 88 may drawelectrical energy from battery 180 to generate the laser energy for anignition event. In the depicted example, engine 20 may be configured ina hybrid electric vehicle that uses motor torque from battery 180 topropel the vehicle during some conditions and engine torque from engine20 to propel the vehicle during other conditions. LCU 90 may receiveoperational instructions from controller 12. As elaborated below, thismay include receiving instructions regarding a current to draw to frombattery 180 to vary the energy of a laser pulse delivered by exciter 88.Laser exciter 88 includes a laser oscillating portion 86 and a lightconverging portion 84. The light converging portion 84 converges laserlight generated by the laser oscillating portion 86 on a laser focalpoint 82 of combustion cylinder 30.

A photodetector 94 may be located in the top of cylinder 30 as part ofthe laser and may receive return pulses from the top surface of piston36. Photodetector 94 may include one or more of a sensor, a camera, anda lens. In one example, the camera is a charge coupled device (CCD)configured to detect and read laser pulses emitted by LCU 90. Forexample, when the LCU emits laser pulses in an infra-red frequencyrange, the CCD camera may operate and receive the pulses in theinfra-red frequency range. In such an embodiment, the camera may also bereferred to as an infrared camera. In other embodiments, the camera maybe a full-spectrum CCD camera that is capable of operating in a visualspectrum as well as the infra-red spectrum.

The camera may include a lens for focusing the detected laser pulses. Inone example, the lens is a fish-eye lens. After laser emission from LCU90, the laser sweeps within the interior region of cylinder 30 at laserfocal point 82. As such, following operation of the laser ignitiondevice, due to ignition of an air-fuel mixture in the cylinder, acylinder combustion event may occur and a cylinder temperature may rise.Thus, light energy that is reflected off of piston 36 and heat generatedin the cylinder may be detected by the infra-red camera in photodetector94. In this way, the photodetector may be used to provide informationregarding the quality of combustion in the cylinder. For example, thephotodetector may provide information regarding the flame front, theflame quality and other combustion parameters.

In another example, the photodetector may include an infra-red sensor.The output of the photodetector in the infra-red spectrum may be used toestimate and monitor a flame quality in the cylinder. Specifically,following a combustion event, a peak in-cylinder temperature achievedmay be estimated or inferred based on the output of the photodetector inthe infra-red spectrum. If the temperature achieved is sufficiently high(e.g., higher than a threshold temperature), good cylinder combustionand delivery of sufficient laser ignition energy during the completedcombustion/ignition event may be determined. In comparison, if thetemperature achieved is not sufficiently high (e.g., lower than thethreshold temperature), insufficient or incomplete combustion anddelivery of insufficient laser ignition energy during the completedcombustion/ignition event may be determined.

It will be appreciated that in still further embodiments, the flamequality may be monitored by comparing a cylinder temperature profileestimated by the photodetector in the infra-red spectrum to an expectedcylinder temperature profile. The expected in-cylinder temperatureprofile may reflect heat generated in the cylinder and/or released fromthe cylinder over the course of a cylinder combustion event. Forexample, the cylinder temperature may be lower during an intake strokewhen fresh intake air is received in the cylinder. Then, during acompression stroke, as an air-fuel mixture is compressed, a slightincrease in temperature may be observed. Following the laser ignitionevent, during a compression stroke, ignition of the compressed air-fuelmixture may lead to combustion and a sudden increase in cylindertemperature. Finally, during an exhaust stroke, as the products ofcombustion are released from the cylinder, a cylinder temperature mayfall. Thus, if combustion occurs in the cylinder as expected, a cylindertemperature profile with a peak at or around the compression stroke, ata threshold time since the laser ignition event, may be observed. As aresult, the expected combustion profile may include an in-cylinder peaktemperature that is higher than a threshold temperature and/or a peaktemperature that occurs at a timing that is after a threshold durationsince the laser ignition event. In the event of degraded combustion(e.g., a misfire event), an amount of heat generated in the cylinder maybe substantially lower. Thus, the peak in-cylinder temperature may belower than the threshold temperature. Further, a timing of the peaktemperature in the temperature profile may lie outside of (e.g., laterthan) the threshold duration since the operation of the laser ignitiondevice. Based on the discrepancy, degraded flame quality may bedetermined. As elaborated herein, responsive to the degraded flamequality, a laser intensity of the laser ignition system may be adjusted.

Laser system 92 is configured to operate in more than one capacity. Forexample, during combusting conditions, laser energy may be utilized forigniting an air/fuel mixture during a power stroke of the engine,including during engine cranking, engine warm-up operation, andwarmed-up engine operation. Fuel injected by fuel injector 66 may forman air/fuel mixture during at least a portion of an intake stroke, whereigniting of the air/fuel mixture with laser energy generated by laserexciter 88 commences combustion of the otherwise non-combustibleair/fuel mixture and drives piston 36 downward. As another example,during non-combusting conditions, the laser energy may be used toidentify the position of a piston of the cylinder, and thereby infer anengine position. Accurate engine position determination may be usedduring an engine start or restart to select a cylinder in which a firstcombustion event is initiated. During the determination of pistonposition, the laser device may sweep laser pulses with low energyintensity. For example, the laser may be frequency-modulated with arepetitive linear frequency ramp to determine the position of one ormore pistons in an engine. Photodetector 94 may detect the light energythat is reflected off of the piston. An engine controller may determinethe position of the piston in the cylinder based on a time differencebetween emission of the laser pulse and detection of the light reflectedoff the piston by the photodetector.

LCU 90 may direct laser exciter 88 to focus laser energy at differentlocations and at different power levels depending on operatingconditions. For example, during combusting conditions, the laser energymay be focused at a first location away from cylinder wall 32 within theinterior region of cylinder 30 in order to ignite an air/fuel mixture.In one embodiment, the first location may be near top dead center (TDC)of a power stroke. Further, the laser pulses used in this ignition modeto initiate cylinder combustion may be of a relatively higher powerlevel. Further still, LCU 90 may direct laser exciter 88 to generate afirst plurality of laser pulses directed to the first location, and thefirst combustion from rest may receive laser energy from laser exciter88 that is greater than laser energy delivered to the first location forlater combustions. In comparison, during non-combusting conditions, thelaser energy may be focused at a top of the piston surface. The laserdevice may sweep laser pulses with low energy intensity through thecylinder at a high frequency. For example, the laser may befrequency-modulated with a repetitive linear frequency ramp. The laserpulses used when operating in piston determination mode may be of alower power level than the laser pulses used when operating in theignition mode.

As elaborated below, controller 12 controls LCU 90 and hasnon-transitory computer readable storage medium including code to adjustthe intensity of laser energy delivery based on, for example, monitoredflame quality, engine load, cylinder head temperature, exhaust air-fuelratio and battery state of charge. In addition, a location of deliveringthe laser energy may also be varied. Controller 12 may also incorporateadditional or alternative sensors for determining the operational modeof engine 20, including additional temperature sensors, pressuresensors, torque sensors as well as sensors that detect engine rotationalspeed, air amount and fuel injection quantity.

As described above, FIG. 1 shows only one cylinder of a multi-cylinderengine, and each cylinder may similarly include its own set ofintake/exhaust valves, fuel injector, laser ignition system, etc.

As discussed above, during combustion conditions, the laser system maybe operated in a higher power mode so as to generate sufficient laserenergy to ignite and combust an air-fuel mixture in the cylinders.Energy may be drawn from the system battery 180 to operate the laser.The inventors have recognized that, typically, the laser ignition systemis operated in the higher power level during combustion conditions toensure sufficient laser energy for guaranteed cylinder combustion.However, if the laser ignition device is continually operated in thehigher power mode, at the elevated energy level or intensity, batteryenergy may be drawn at a high rate. This may adversely affecting thefuel economy of the hybrid vehicle. In particular, based on cylinderoperating conditions, and variations in engine load, the laser energyrequired to provide sufficient combustion of a cylinder air-fuel mixturemay vary and may frequently be lower than the elevated (e.g., maximal)level. During those conditions, the use of higher laser intensity may bewasteful.

As elaborated with reference to FIG. 2, during combustion conditions,the controller may decrease (e.g., continually or step-wise) the laserintensity over consecutive ignition events. The intensity may bedecreased by decreasing the current drawn by the laser ignition systemfrom battery 180 by a first factor that is based on engine loadconditions as well as one or more of a battery state of charge, acylinder head temperature, and a cylinder combustion air-fuel ratio. Forexample, as the cylinder had temperature decreases, the laser intensityused may be increased (that is, the first factor may be decreased). Asanother example, as the combustion air-fuel ratio becomes leaner thanstoichiometry, the laser intensity used may be increased (with a smallerfirst factor being applied). The cylinder combustion event following theignition event may be monitored by the photo-detector. If the flamequality is degraded (e.g., less than a threshold), it may be determinedthat the laser energy was not sufficient for efficient combustion.Accordingly, the controller may increase the laser energy level, forexample, by increasing the current drawn by the laser ignition systemfrom the battery by a second factor. The second factor may be smallerthan the first factor and may also depend on engine load. The controllermay then resume reducing the laser energy with smaller sized steps(e.g., with a smaller factor). In this way, the controller maydynamically and continually adjust the laser energy in a closed-loopfashion. This allows laser usage to be significantly reduced, improvingbattery consumption and vehicle fuel economy.

Now turning to FIG. 2, a routine 200 is shown for dynamically adjustinga laser intensity of an engine laser ignition device during a cylinderignition event based on a monitored cylinder flame quality. Theclosed-loop control approach allows battery usage for ignition to bereduced, providing fuel economy benefits in a hybrid electric vehicle.

At 202, it may be determined if the laser ignition system attempted tofire. That is, it may be determined if a laser ignition event occurred.As such, during the laser ignition event, current may be drawn by thelaser ignition system from a vehicle battery for generating laser energyfor the ignition event.

Next, at 204, a peak in-cylinder temperature for a cylinder combustionevent corresponding to the laser ignition event may be estimated and/orinferred. For example, the peak in-cylinder temperature following eachignition event may be inferred based on an output of a photodetector,operating in an infra-red spectrum, the photodetector coupled to thelaser ignition system. The photodetector may include one or more of aninfrared sensor, a CCD camera, and a spectral sensor operating in theinfra-red region. As such, the sensor or photodetector lens may becleaned prior to every combustion event by part of the fuel injectorspray that sprays fuel directly (that is, via direct injection) into thecylinder. During the combustion event following the ignition event, heatis generated which produces infra-red light that is sensed by thephotodetector. Based on the output of the photodetector, a cylinderflame quality (and other cylinder combustion parameters) for acombustion event resulting from the laser ignition event may bemonitored.

At 206, it may be determined if the measured or inferred in-cylinderpeak temperature is indicative of good cylinder combustion. For example,it may be determined if the temperature is higher than a threshold.Optionally, it may also be determined if a timing of the peaktemperature is at a time corresponding to a compression stroke of thecylinder. If yes, then at 208, it may be determined that the monitoredflame quality of the combustion event resulting from the preceding laserignition event (at 202) is good and not degraded. In response to theflame quality not being degraded, and to optimize the use of laserenergy, also at 208, the controller may decrease the laser intensity. Inone example, decreasing the laser intensity includes step-wisedecreasing the laser intensity over multiple ignition events (e.g., eachsubsequent ignition event) with a first factor based at least on engineload. This is because the ignition energy required for sufficientcombustion in a cylinder varies with engine parameters such as engineload. As an example, as the engine load increases, the first factor maybe decreased since higher engine load conditions typically require moreignition energy for good combustion. The first factor may be furtherbased on one or more of a cylinder head temperature, combustion air-fuelratio, and battery state of charge. By adjusting the first factor, asize of the step used in the step-wise reduction of laser intensity canbe varied. In particular, a higher laser intensity may be applied atcolder cylinder head temperatures. Likewise, a higher laser intensitymay be applied during leaner cylinder operation. In alternate examples,the laser intensity may be gradually decreased and a rate of the gradualdecrease may be adjusted based on one or more of the cylinder headtemperature, the combustion air-fuel ratio and the battery state ofcharge. Further still, the laser intensity may be reduced and thenmaintained at the reduced level for a number of ignition events, thenfurther reduced and then maintained at the further reduced level for anumber of ignition events, and so on.

From 208, the routine returns to 202 to resume reconfirming ignition andgood combustion before further reducing the laser intensity. In thisway, following a laser ignition event of the engine, the controller mayreduce a laser intensity at a plurality of subsequent laser ignitionevents of the engine until an inferred combustion flame quality reachesa threshold, the inferred combustion flame quality based on aphotodetector coupled to the laser ignition system.

If good combustion is not confirmed at 206, at 210 it may be confirmedthat the measured temperature (or monitored flame quality) indicatedinsufficient combustion. That is, it may be confirmed that the monitoredflame quality for the combustion event was degraded. If not, the routinereturns to 202 to resume reconfirming ignition and good combustionbefore further reducing the laser intensity. If degraded flame qualityis confirmed, then at 212, the routine includes increasing the laserintensity. Increasing the laser intensity may include, for example,step-wise increasing the laser intensity over each ignition event with asecond factor, different from the first factor used for decreasing thelaser intensity. The second factor may also be based on engine load. Forexample, as the engine load increases, the second factor may beincreased.

As used herein, decreasing the laser intensity includes decreasing acurrent of the laser ignition system during each ignition event, whileincreasing the laser intensity includes increasing the current of thelaser ignition system during each ignition event. Specifically, duringthe decreasing, the current of the laser ignition device may bedecreased by the first factor while during the increasing, the currentof the laser ignition device may be increased by the second factor.Further, the first factor applied during the decreasing of laserintensity may be larger than the second factor applied during theincreasing of laser intensity. In other words, the laser energy may bedecreased by larger steps until combustion is degraded and then theintensity may be incremented by smaller steps. This allows the laserenergy usage to be fine-tuned and optimized.

It will be appreciated that while the routine of FIG. 2 depicts, at eachignition event, decreasing the laser intensity and monitoring thecylinder flame quality, and then increasing the laser intensity at thenext ignition event if the cylinder flame quality was determined to bedegraded, it will be appreciated that in alternate examples, the laserintensity may be increased only after a threshold number of degradedcombustion events have been confirmed. For example, the controller may,at each ignition event, decrease the laser intensity until the monitoredcylinder flame quality is degraded over a threshold number ofconsecutive ignition events (such as 1-2 consecutive combustion events),and then increase the laser intensity.

As discussed above, it may be determined that the monitored flamequality is degraded based on an inferred peak in-cylinder temperaturebeing lower than a threshold. However, it will be appreciated that whilethe routine of FIG. 2 assesses cylinder combustion and flame qualitybased on inferred in-cylinder peak temperatures and uses the assessmentto vary the laser intensity for subsequent laser ignition events, inalternate embodiments, the inferred in-cylinder peak temperature may beused to assess one or more other, or additional, cylinder combustionparameters and that assessment may be used to vary the laser intensityfor subsequent laser ignition events.

After the increasing, the routine may return to 202 to resume decreasingthe laser intensity towards a minimal level. Optionally, afterincreasing the laser intensity, on the next iteration of the routine,the first factor may be reduced. In other words, a larger first factormay be applied when decreasing the laser intensity before degradedcombustion is identified and before the laser intensity iscompensatorily increased, while a smaller first factor may be appliedwhen decreasing the laser intensity after degraded combustion isidentified and after the laser intensity has been increased. Forexample, after increasing the laser intensity, the controller may reducethe first factor and repeat the decreasing of the laser intensity untilthe monitored cylinder flame quality is degraded with the reduced firstfactor.

From 212 the routine may also proceed to 214 to determine if there isany sudden change in engine load. As such, changes in engine load maylead to variations in the amount of ignition energy required for goodcylinder combustion. Thus at 214, it may be determined if there is asudden increase in engine load. This may include determining if theengine load is higher than a threshold, or if a rate of increase in theengine load is larger than a threshold (rate). If yes, then at 218, theroutine includes, increasing the second factor and/or decreasing thefirst factor. That is, responsive to the rapid increase in engine load,which may require more ignition energy, the increasing of laserintensity (as at 212) is done at a higher rate and with larger steps sothat more ignition energy can be provided at the higher load condition.Alternatively, the decreasing of laser intensity (as at 208) is done ata lower rate and with smaller steps so that more ignition energy isavailable at the higher load condition. In a further example, responsiveto the sudden increase in engine load, the controller may resumeoperating the laser ignition system at the maximal ignition energy level(e,g., for a number of combustion events) to ensure sufficientcombustion at the high load conditions. The decreasing may then beresumed when the engine load has decreased.

If there is no sudden increase in engine load, at 216, the routinedetermines if any abnormal combustion event has occurred. For example,it may be determined if there is an indication of severe misfire, orpre-ignition. As such, one or more of these abnormal combustion eventsmay be induced by insufficient ignition energy. Thus, if abnormalcombustion is confirmed, the routine returns to 218 to adjust the laserintensity to reduce further occurrence of abnormal combustion events.Specifically, the decreasing of laser intensity may be performed at aslower and smaller clip while the increasing of laser intensity may beperformed at a faster and larger clip so as to provide more ignitionenergy for the subsequent ignition events. In a further example,responsive to the misfire, the controller may resume operating the laserignition system at the maximal ignition energy level (e,g., for a numberof combustion events) at least until the indication of abnormalcombustion has decreased. If no misfire is determined, the routine mayreturn to 202 and the decreasing of laser intensity to optimize laserenergy usage may be reiterated.

In this way, reduction of laser intensity may be performed as anon-going dynamic process where the flame and combustion quality ismonitored directly by the infra-red photo-detector. By dynamicallyreducing the laser intensity, energy can be saved over a drive cycle.

In one example, a method for a hybrid vehicle engine including a laserignition system comprises, following a laser ignition event of theengine, reducing a laser intensity at a plurality of subsequent laserignition events of the engine until an inferred combustion flame qualityreaches a threshold, the inferred combustion flame quality based on aphotodetector coupled to the laser ignition system; and then increasingthe laser intensity responsive to reaching the threshold. Thephotodetector may be configured for infra-red detection. Inferring acombustion flame quality based on the photodetector may includeestimating a peak in-cylinder temperature following each laser ignitionevent based on an output of the photodetector and inferring thecombustion flame quality is degraded when the estimated peak in-cylindertemperature is lower than a threshold. Reducing the laser intensity mayinclude reducing a current delivered to the laser ignition system from abattery by a first factor, the reduction factor based at least on engineload. The first factor may be further based on a state of charge of thebattery, the first factor decreased as the battery state of chargedecreases. The first factor may be further based on a cylinder headtemperature and an exhaust air-fuel ratio, the first factor decreased asthe cylinder head temperature falls or the air-fuel ratio falls becomesleaner than stoichiometry. Increasing the laser intensity may includeincreasing the current delivered to the laser ignition system by asecond factor, the second factor based on the first factor and a rate ofchange in engine load. The second factor may be increased as a rate ofrise in engine load increases. The first factor may be decreased and/orthe second factor may be increased in response to one or more of anengine misfire event, and a pre-ignition event.

Now turning to FIG. 3, an example laser intensity adjustment over avehicle drive cycle is shown. Map 300 depicts engine operation at plot302, changes in laser ignition intensity at plot 304, cylinder flamequality at plot 306, and engine load at plot 308.

Prior to t1, the engine may be off. At t1, engine operation may beresumed (plot 302) and laser ignition may be required. Accordingly, att1, a laser ignition device may be actuated on and the laser intensitymay be initially set to a highest setting. The laser intensity of theengine laser ignition device may be dynamically adjusted from thehighest setting over cylinder ignition events based on a monitoredcylinder flame quality. Specifically, between t1 and t2, at each(consecutive) ignition event, the laser intensity may be step-wisedecreased until the monitored cylinder flame quality is degraded over athreshold number of consecutive ignition events. The step-wise decreasemay be based on the engine load (plot 308). In the depicted example, thecylinder flame quality may be determined based on an inferred peakin-cylinder temperature. The temperature may be based on the output of aphotodetector coupled to the laser ignition device, the photodetectoroperating in an infra-red spectrum.

During the ignition event immediately before t2, as the ignitionintensity is decreased, cylinder flame quality may become degraded andfall below threshold 307. The controller may then infer that the laserintensity is too low and in response to the degraded flame quality, thelaser intensity may be increased at t2. The increase may also bestep-wise but may be smaller than the preceding step-wise decrease. Inresponse to the increase in laser intensity, the flame quality mayimprove.

Between t2 and t3, the laser intensity may be further optimized byreiterating the dynamic adjustment of the laser intensity. Specifically,between t2 and t3, the laser intensity may be step-wise decreased withthe size of the step-wise decrease adjusted to be smaller than the sizeof the step-wise decrease performed between t1 and t2. In addition tobeing shallower, the steps may also be longer. In other words, the laserintensity may be decreased by a smaller amount and then held at thereduced intensity for a number of ignition events (e.g., 1-2 events)before the intensity is decreased again.

At t3, a misfire event may be indicated. In response to the misfireindication, the laser intensity may be increased and held at theincreased level until the indication of misfire is reduced at t4. At t4,it may be determined that the engine load is increasing. To providesufficient ignition energy to provide good combustion during theelevated engine load conditions, at t4, the laser intensity may beincreased. The laser intensity may then resume the dynamic adjustmentwith the intensity step-wise decreased between t4 and t5. Herein, a sizeof the steps used to decrease the intensity may be smaller than the sizeof the steps used to decrease the intensity between t1 and t2, when theengine load was lower. At t5, the engine load may decrease and thedynamic adjustment of the laser intensity with the larger steps may beresumed. In this way, laser energy usage can be optimized.

In one example, a hybrid vehicle system comprises an engine including acylinder, the cylinder including a piston, an electric motor-generatorcouple to a battery, a battery-operated laser ignition device coupled toa cylinder head, and a photodetector configured for infra-red detectioncoupled to the laser ignition device. A vehicle controller may beconfigured with computer readable instructions for: at each ignitionevent, estimating a flame quality inside the cylinder using thephotodetector, and in response to the estimated flame quality beinghigher than a threshold, reducing a laser intensity of the laserignition device at a subsequent ignition event. Further, in response tothe estimated flame quality being lower than the threshold, thecontroller may increase the laser intensity of the laser ignition devicefor a threshold number of ignition events. As used herein, reducing alaser intensity of the laser ignition device includes drawing a smallercurrent from the battery into the laser ignition device, whileincreasing the laser intensity of the laser ignition device includesdrawing a larger current from the battery into the laser ignitiondevice.

In this way, laser energy usage can be fine-tuned to reduce energyconsumption and improve hybrid vehicle fuel economy. By reducing thelaser intensity for an ignition event towards a minimal level withoutdegrading combustion parameters such as flame quality, laser energyusage is reduced. By close-loop adjusting the laser intensity based onthe flame quality, rather than open-loop adjusting the laser intensity,the need to provide excess laser energy to guarantee flame quality isreduced. This reduces consumption of battery power during laseractuation and improves fuel economy in a hybrid vehicle system.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The specific routines described herein may represent one or more of anynumber of processing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various actions,operations, and/or functions illustrated may be performed in thesequence illustrated, in parallel, or in some cases omitted. Likewise,the order of processing is not necessarily required to achieve thefeatures and advantages of the example embodiments described herein, butis provided for ease of illustration and description. One or more of theillustrated actions, operations and/or functions may be repeatedlyperformed depending on the particular strategy being used. Further, thedescribed actions, operations and/or functions may graphically representcode to be programmed into non-transitory memory of the computerreadable storage medium in the engine control system.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

The invention claimed is:
 1. An engine method, comprising: dynamicallyadjusting a laser intensity of an engine laser ignition device during acylinder ignition event via closed-loop control based on a monitoredcylinder flame quality, increasing an amount of current drawn from abattery of an engine into the laser ignition device to increase thelaser intensity, and decreasing the amount of current drawn from thebattery of the engine into the laser ignition device to decrease thelaser intensity.
 2. The method of claim 1, wherein the dynamicallyadjusting includes, at each ignition event, decreasing the laserintensity until the monitored cylinder flame quality is degraded over athreshold number of consecutive ignition events, and then increasing thelaser intensity.
 3. The method of claim 2, wherein decreasing the laserintensity includes step-wise decreasing the laser intensity over eachignition event with a first factor based on engine load.
 4. The methodof claim 3, wherein increasing the laser intensity includes step-wiseincreasing the laser intensity over each ignition event with a secondfactor based on engine load.
 5. The method of claim 4, wherein the firstfactor applied during the decreasing is larger than the second factorapplied during the increasing.
 6. The method of claim 5, furthercomprising, after increasing the laser intensity, reducing the firstfactor and repeating the decreasing the laser intensity until themonitored cylinder flame quality is degraded with the reduced firstfactor.
 7. The method of claim 5, further comprising, in response to arate of increase in engine load being larger than a threshold,increasing the second factor or decreasing the first factor.
 8. Themethod of claim 2, wherein decreasing the laser intensity includesdecreasing the current drawn into the laser ignition device during eachignition event, and wherein increasing the laser intensity includesincreasing the current drawn into the laser ignition device during eachignition event.
 9. The method of claim 1, further comprising, monitoringthe cylinder flame quality via a photodetector coupled to the laserignition device, the monitoring including inferring a peak in-cylindertemperature following each ignition event based on an output of thephotodetector.
 10. The method of claim 9, wherein monitoring thecylinder flame quality with the photodetector includes monitoring thecylinder flame quality with a photodetector that includes one or more ofan infrared camera, a CCD camera, and a spectral sensor.
 11. The methodof claim 9, wherein the monitored cylinder flame quality being degradedincludes the inferred peak in-cylinder temperature being lower than athreshold.
 12. A method for a hybrid vehicle engine including a laserignition system, comprising: following a laser ignition event of theengine, reducing a laser intensity at a plurality of subsequent laserignition events of the engine until an inferred combustion flame qualityreaches a threshold, the inferred combustion flame quality based on aphotodetector coupled to the laser ignition system; and then increasingthe laser intensity responsive to reaching the threshold, wherein thephotodetector is configured for infra-red detection and wherein theinferred combustion flame quality based on the photodetector includesestimating a peak in-cylinder temperature following each laser ignitionevent based on an output of the photodetector and the inferredcombustion flame quality is degraded when the estimated peak in-cylindertemperature is lower than a threshold.
 13. The method of claim 12,wherein reducing the laser intensity includes reducing a currentdelivered to the laser ignition system from a battery by a first factor,the reduction factor based at least on engine load.
 14. The method ofclaim 13, wherein the first factor is further based on one or more of acylinder head temperature, an exhaust air-fuel ratio, and a state ofcharge of the battery.
 15. The method of claim 13, wherein increasingthe laser intensity includes increasing the current delivered to thelaser ignition system by a second factor, the second factor based on thefirst factor and a rate of change in engine load.
 16. The method ofclaim 15, wherein the second factor is increased as a rate of rise inengine load increases.
 17. The method of claim 16, wherein the firstfactor is decreased and/or the second factor is increased in response toone or more of an engine misfire event and a pre-ignition event.
 18. Ahybrid vehicle system, comprising: an engine including a cylinder, thecylinder including a piston; an electric motor-generator coupled to abattery; a battery-operated laser ignition device coupled to a cylinderhead; a photodetector configured for infra-red detection coupled to thelaser ignition device; and a controller with computer readableinstructions for: at each ignition event, estimating a flame qualityinside the cylinder using the photodetector; in response to theestimated flame quality being higher than a threshold, reducing a laserintensity of the laser ignition device at a subsequent ignition event;and in response to the estimated flame quality being lower than thethreshold, increasing the laser intensity of the laser ignition devicefor a threshold number of ignition events, wherein reducing the laserintensity of the laser ignition device includes drawing a smallercurrent from the battery into the laser ignition device, and whereinincreasing the laser intensity of the laser ignition device includesdrawing a larger current from the battery into the laser ignitiondevice.